1. Field of the Invention
The present invention relates generally to a wavelength converting device for obtaining, for example, a second order harmonic by converting the wavelength of a light beam such as a laser, and more specifically to a wavelength converting device having a substrate composed of spinel and a waveguide formed of a KNbO.sub.3 layer and a method of fabricating the wavelength converting device.
2. Description of the Related Art
A wavelength converting device has a function of radiating a second order harmonic of a laser. This is preferably utilized for obtaining a laser having a shorter wavelength. A typical wavelength converting device has: a substrate composed of spinel (for example, MgO.Al.sub.2 O.sub.3); a waveguide formed of a KNbO.sub.3 layer, which is formed on the substrate by crystal growth; an electrode layer formed on the surface of the KNbO.sub.3 layer; and a stripe-shaped TiO.sub.2 layer which is used to shut the light therein and which is formed on the surface of the KNbO.sub.3 layer. The KNbO.sub.3 layer has characteristics that a nonlinear optical constant is large and that a light damage resistance is high. Therefore, this type of the wave converting device enables high efficient wavelength conversion and has a long life.
However, this type of wave converting device has a problem that deformation occurs in the KNbO.sub.3 layer because the lattice constant of the KNbO.sub.3 layer is mismatched with that of the spinel (namely, a multiple of the lattice constant of KNbO.sub.3 layer is mismatched with that of the spinel). This causes a loss to propagation of a light.